Apache JMeter is a 100% pure Java desktop application designed to
load test functional behavior and measure performance. It was
originally designed for testing Web Applications but has since
expanded to other test functions.

Apache JMeter may be used to test performance both on static and
dynamic resources (files, Servlets, Perl scripts, Java Objects,
Data Bases and Queries, FTP Servers and more). It can be used to
simulate a heavy load on a server, network or object to test its
strength or to analyze overall performance under different load
types. You can use it to make a graphical analysis of performance
or to test your server/script/object behavior under heavy
concurrent load.

In addition to load-testing, the tool can also be used to verify
correctness of your web-applications.